An internal-combustion engine's cylinder bore is a large hole machined inside an engine block, in order to guide the engine piston as it performs its reciprocating motion. In cooperation with the cylinder head, the cylinder bore enables the performance of intake, compression, power and exhaust strokes by the engine piston. The cylinder bore known in the prior art is most commonly machined through the top of the engine block and is slightly larger than the piston to provide a clearance between the two. This clearance allows the piston to move freely in the cylinder. Piston rings are provided to seal the clearance between the cylinder wall and the piston. Since the piston's reciprocating motion inside the cylinder causes a great deal of friction between the cylinder wall and piston rings, the cylinder bore in the prior art is machined with a completely smooth surface. Said friction is caused by forces which act along the engine's connecting rod due to the change of its angle while converting the reciprocating motion of the piston into the rotary motion of the crankshaft. This motion produces side thrust on the piston, thus causing it to shift toward a major thrust face (i.e., the piston presses against a portion of the cylinder wall).
Therefore, the piston rings create taper wear on the cylinder wall. The side thrust does not allow any opening to be machined on any thrust face of the cylinder wall, except in the case of two-stroke engines, wherein intake and exhaust ports are machined in the bottom of the cylinder wall's stroke section.
As proposed in the invention entitled "Hydraulic connecting rod" by the same authors, disclosed to U.S. Patent Office on Apr. 5th, 1989, Ser. No. 07/333,685, the hydraulic connecting rod allows transmission of combustion force without producing any side thrust on the engine piston and, consequently, allows the engine piston to perform its reciprocating motion without causing friction between its rings and the cylinder wall. Therefore, the engine piston can be machined accurately enough to maintain a good seal with the cylinder wall and to prevent excessive "blow-by" of unburned air-fuel mixture and burned gases from the combustion chamber. Since the engine piston slides up and down inside the cylinder wall without any side thrust, the openings can be machined inside the cylinder wall without risking any damage, either of said wall or said piston and its rings. Therefore, additional valve ports and an additional combustion chamber can be machined inside the cylinder wall, in order to obtain excellent volumetric efficiency and allow a two-step combustion process which will result in significantly increased force produced by the cylinder's combustion pressure and better burning of the compressed air-fuel mixture.
There are numerous methods disclosed in the prior art for enhancing the burning of the air-fuel mixture and reducing emissions produced during the engine's combustion cycle. Since the formation of emissions significantly depends on the air-fuel ratio and compression ratio, some of the methods known in the prior art such as the so-called Honda system, comprise a two-step combustion process wherein air-fuel mixtures burned inside precombustion and combustion chambers have different air-fuel ratios. This ensures good burning of the fuel, so that polluting gases are kept to a low level, but does not have a positive effect on the force produced by combustion pressure. Combustion processes in the prior art provide high combustion pressure which significantly drops after about 30 degrees past engine piston's top dead center (TDC), wherein inertia and centrifugal loads strongly influence the combustion pressure's resultant force.
According to the process of the present invention, an additional combustion chamber machined inside the cylinder wall ensures good burning of the fuel and produces additional combustion pressure during that portion of the piston's power stroke, wherein the resultant load significantly decreases due to sudden drop of the combustion pressure.